The present invention relates to a device for detecting clogging of a video tape recorder recording head that carries out recording helically with respect to the longitudinal direction by means of a head provided on a rotating cylinder.
Conventionally, as shown in FIG. 17, a camcoder records by means of a rotating head along a magnetic tape 31 around a cylinder 36. In order to verify the recorded state upon recording, as for a signal recorded on recording tracks 37 of the magnetic tape 31, an information signal 35, which has been recorded by a recording head 33 immediately before, is reproduced by a reproducing head 32 for detecting clogging. The reproducing head 32 is positioned to follow the recording head 33. When a recording failure results from clogging of the head, etc., the clogging is detected immediately and cleaning and so on is performed on the head. Reference numeral 38 denotes a running direction of the magnetic tape 31 and reference numeral 39 denotes a tracing direction of the recording head 33 and so on. An erase head 34 erases an area in advance for recording the information signal 35 ahead of the recording head 33. Thus, it is possible to eliminate the influence of a previously recorded signal.
As equipment decreases in size, a VTR system having a small cylinder diameter has been put into practice. Meanwhile, in accordance with the trend toward high-quality images, the signal transfer rate increases. Hence, it has been necessary to reduce the number of heads per cylinder to maintain the same number of revolutions of the cylinder. Meanwhile, it is difficult to mount a number of sets of heads on a single cylinder where each set includes an erasing head, a recording head, and a reproducing head.
However, regarding a recording/reproducing apparatus, it is quite important for the device to operate normally by recording and verifying the recording. Except in cases where recorded information can be read repeatedly, for example, when recording an event taking place only one time for news reports and so on, it is important to verify the operating state of the recording device upon recording. As a conventional technique for collecting materials for news reports using a camera and a VTR, the following method has been mainly used: just before recording, recording and playback is performed for a short time on a tape to be recorded, and then the recording/reproducing operation is verified. Or a recording head and a reproducing head, which reads recorded information immediately after the recording, are provided in the functionality of the VTR, and the recording operation is verified by reading recorded information while recording.
The above function, which verifies recorded information by performing reproduction immediately after recording, is a function essential to an external memory for a computer and a camcorder for acquisition by broadcasters.
Moreover, as a simple method of verifying the recording operation, the following method has been also adopted as a conventional technique: when the recording operation is verified by reproduction immediately after recording, instead of playback all recorded data to make a comparison with the original data, the presence or absence of an envelope of reproduction output is detected after recording.
As for the verification of the recording function, the method of performing recording and reproducing on a tape just before recording is actually limited by the amount of time available. Additionally, no solutions are possible in the event of a malfunction during the recording process.
Also, when information is read immediately after recording, a reproducing head is necessary for verifying the recording process in addition to a recording head.
In general, a means for achieving high-quality recording/reproducing output is that an erasing head completely demagnetizes a tape just before recording; the tape is initialized; and recording is carried out. Thus, in order to realize more reliable recording, three kinds of heads are necessary which include a recording head, a reproducing head, and an erasing head.
Generally in a VTR using a helical scanning method, by which a tape is wrapped around 180-degrees of the cylinder and is recorded and reproduced, a pair of heads (two heads) are positioned opposing each other at 180-degree angles on the rotary cylinder, and the heads are switched at every half turn for recording. In this case, six heads are necessary in total.
Furthermore, in the case where recorded information has a high data rate and recording is not carried out by a single recording head system but by a two heads system, twelve heads are required in total. Hence, a problem appears in packaging so many heads together. Additionally, in the case of n-channel recording system, since 6xc3x97n heads in total need to be installed on the cylinder, it is not possible to mount all the heads when building a VTR.
An object of the present invention is to provide a recording head clogging detection method, by which the above clogging can be detected without providing a reproducing head for detecting clogging of the recording head. Therefore, the recording head clogging detection method of the present invention is characterized in that an erasing head records a test signal in a specific section of a recording track, evaluation is made on a reproduced test signal obtained by reproducing the test signal in the recording head, and the occurrence of clogging is evaluated. According to the present invention, it is possible to detect the occurrence of clogging of the recording head without the necessity for a reproducing head used for detecting clogging of the recording head.
Furthermore, a preceding first head records sub information in a second area. When a second head records main information in a first area, the sub information is reproduced from the second area. It is possible to detect the presence or absence of adherents on the head based on the reproduction output. Furthermore, at the same time, verification is made on the reliability of the recording operation by verifying recording current, which is applied when the second head records main information. Hence, even if the number of heads installed in a rotary cylinder is reduced, it is possible to verify the recording. Namely, the present invention is realized as follows: regarding contamination (adherent such as tape fillings adhered to a surface of the head) that degrades the reliability of a recording/reproducing system of the tape head, a detection signal is recorded and reproduced in a predetermined area by using the positional relationship between the first head (e.g., an erasing head) and the second head (e.g., a recording head).
The following will discuss the detail of the present invention.
The recording head clogging detection method of the present invention is characterized in that a magnetic recording/reproducing apparatus reproduces from a magnetic tape having an information signal recorded by rotating and scanning the heads in sequence, the signal being provided helically with respect to the longitudinal direction of a magnetic tape. When detecting clogging of a recording head, a test signal is recorded on the magnetic tape by applying current with a frequency lower than an erasing frequency to an erasing head which erases an area for recording an information signal before the recording head records information in a recording track for each recording track, every specified number of two or more recording tracks, or every specified time, at a timing when the erasing head traces a specific section of the area for recording an information signal in the recording track; and the presence or absence of clogging of the recording head is determined by evaluating the reproduced test signal obtained by reproducing the test signal, which is recorded by the erasing head, by means of the recording head.
Moreover, the method of the present invention is characterized in that the specific section for recording a test signal is at least one of the sections in the beginning and the end of the area for recording an information signal in the recording track.
Furthermore, the method of the present invention is characterized in that when a track pitch is W (xcexcm) and a difference in azimuth angle is xcex8 (radian) between the erasing head and the recording head, a wavelength xcex(xcexcm) of the test signal is set longer than xcex=xcfx80Wxcex8/6.
As described above, according to the recording head clogging detection method of the present invention, the erasing head records a test signal in the specific section of the recording track on the magnetic tape, and the presence or absence of clogging of the recording head is determined by evaluating the reproduced test signal, which is obtained by reproducing the test signal by the recording head. Thus, the following advantageous effects can be achieved: a reproducing head for detecting clogging is not necessary; a surface of the head can be monitored while recording with a small number of heads including the erasing head and the recording head; and recording can be performed positively with a simple cylinder configuration and a small number of rotary transformers.
Additionally, in the magnetic recording/reproducing apparatus which reproduces from the magnetic tape having an information signal recorded by rotating and scanning the heads in sequence, the signal being provided helically with respect to a longitudinal direction of the magnetic tape, a recording head clogging detector of the present invention is characterized by comprising a signal selecting means for selecting an erasing signal and a test signal, which is lower than the erasing signal in frequency, and applying the signals to the erasing head for erasing an area in which the recording head records an information signal. A control means for instructing the signal selecting means to apply the test signal to the erasing head for each recording track, every specified number of two or more recording tracks or every specified time, at a timing when the erasing head traces at least one of the sections in the beginning and end of the area for recording the information signal in the recording track. An evaluation means for determining the presence or absence of clogging of the recording head by evaluating the reproduced test signal obtained by reproducing the test signal, which is recorded by the erasing head, by means of the recording head.
Furthermore, the detector of the present invention is characterized in that when a track pitch is 18 xcexcm and a difference in azimuth angle is 20xc2x0 between the erasing head and the recording head, a wavelength of the test signal is set longer than 3 xcexcm.
A recording verification method of the present invention is associated with a recording/reproducing apparatus in which heads mounted on a rotary cylinder scan a tape in a helical direction, a track is formed on the tape, and information is recorded and reproduced. The heads include a first head and a second head, and the track includes a first area and a second area. The first head erases the first area and records sub information in the second area. The second head records main information in the first area and reproduces sub information of the second area. The reliability of the recording operation is judged based on a first detection signal and a second detection signal. The first detection signal is produced from the sub information reproduced by the second head, and the second detection signal is produced from current applied to the second head when main information is recorded in the first area. Hence, as for the number of heads, only two kinds of a first head (e.g., an erasing head) and a second head (e.g., a recording head) are necessary. Additionally, the sub information recorded by the first head is reproduced by the second head. Thus, in the case where adherents exist on a surface of the first head or the second head, since a reproduction output level of the second head is lowered, a recording failure can be detected. Moreover, verification can be made on an operation of the recording process by verifying the flow of recording current.
The method of the present invention is characterized in that the first head erases the first area and records sub information in the second areas at once on two tracks, the second head records main information in the first area and reproduces the second areas by means of adjacent paired heads on each track, and the second areas are in the beginning and end of the first area.
The present invention includes a method characterized in that out of the paired heads of the second head, the preceding heads reproduce sub information from the second area placed at the beginning of the first area, the subsequent heads reproduce sub information from the second area placed at the end of the first area, and a first detection signal is produced from these pieces of sub information; and a method characterized in that after the preceding heads of the paired heads of the second head record main information, a recording leakage signal of the subsequent heads is reproduced, and a leakage signal of the preceding heads is reproduced before main information is recorded by the subsequent heads of the paired heads of the second head, thereby producing a second detection signal. With the above methods, even in the case where a recording channel is doubled to improve a recording rate and the number of heads increases so as to permit recording with two channels, the recording state can be verified.
Also, the method is characterized in that when the first head and the second head are different in azimuth angle, a track pitch is W, and a difference in azimuth angle is xcex8, sub information recorded by the first head is substantially a single wavelength xcex represented by xcex=2xc3x97Wxc3x97tan xcex8.
Moreover, the method is characterized in that while the second head reproduces sub information, current applied to the first head is interrupted or reduced. Hence, an SN ratio of the detection signal can be improved.
Additionally, the method is characterized in that the second area for recording sub information is equal to or less than 3% of the first area for recording main information. Thus, the ratio can be set within a suitable range relative to a recording density and capacity of detecting a signal.
According to the recording verification method of the present invention, the first head erases the first area and records sub information in the second area, the second head records main information in the first area and reproduces the sub information of the second area, and the reliability of the recording operation is judged based on the sub information reproduced by the second head and recording current upon recording of the second head. Consequently, it is possible to detect a malfunction caused by the recording head in a recording state.